As is well known in the prior art, an engine starter normally includes a starter motor having an armature and an output shaft with a drive pinion slidably mounted on the output shaft which is caused to engage and drive an engine gear. In recent years, however, in response to the national fuel economy standards, the automobile manufacturers have been downsizing their products. This has created an additional requirement that starter motors be as compact as possible in order to permit the greatest utilization of underhood space in these vehicles. This is particularly important in front wheel drive applications where not only the engine but the transmission and the transaxle are located at the front of the vehicle. Thus, a more compact engine starter drive is highly desirable for any new automotive application. In addition, in response to foreign competition, the automotive manufacturers are requiring lower costs, better reliability, and more serviceable construction.
In prior art starters, such as U.S. Pat. No. 2,979,961 to Glenn S. Spencer, when the pinion is fully or partially in mesh with the ring gear of the engine, a detent will radially engage a notch or recess formed in the screw shaft, thus insuring continuing pinion mesh until the engine is reliably started; yet allowing sufficient axial movement of the screw shaft to enable the one way clutch teeth to overrun. During initial application of torque to the engine ring gear, the screw jack action between a control nut and screw shaft will axially force the clutch members in a demeshing direction. This screw jack action must be absorbed by an elastically deformable compression ring element which is compressively confined between a thrust plate mounted near the clutch and a second thrust plate mounted on the power shaft. This configuration, however, leads to a very long gearing device which is not suitable for present day automotive applications.
Buxton, U.S. Pat. No. 2,933,926, issued Apr. 26, 1960, to the assignee of the present application poses a similar engine starter drive wherein a resilient member is replaced with a series of coupling members which are designed to flip if a predetermined maximum torque is exceeded at the initiation of the cranking operation. This again leads to a very long starter drive configuration.
Another similar engine starter device is disclosed in U.S. Pat. No. 2,901,912, also owned by the assignee of the present invention. This device, which is similar to the device described in U.S. Pat. No. 2,933,926 also incorporates a frictional coupling, the torque capacity of which is directly and positively controlled by means which are a function of the load transmitted to it. This device also provides a very long starter gearing device envelope.
Another prior art device which is similar to the aforementioned starter devices is U.S. Pat. No. 2,922,307, issued to Buxton on Jan. 26, 1960, wherein a rubber block is incorporated into the starter drive as a yielding transmission element. Thus, the pinion is meshed with the engine gear. Further rotation of the power shaft causes the control nut to compress the elastic block and apply torque to the elastic block to yieldably rotate the pinion. The compression of the elastic member causes the chambers formed in the block to be flattened out with the consequent establishment of the sealing attachment to the closed end of the retainer cap and the control nut on the opposite end. This drive also provides a very long envelope which is undesirable for present day automotive applications.
Other prior art starter drives of this type are disclosed in U.S. Pat. No. 2,902,864 to Digby; and U.S. Pat. No. 2,996,924, issued to Sabatani; both owned by the assignee of the present application.
Perhaps the most popular starter drive used to date is disclosed in U.S. Pat. No. 3,222,938, issued to Digby on Dec. 14, 1965. This patent is also owned by the assignee of the present application. Digby discloses a engine starter drive having a power shaft with a shoulder formed thereon and defining a pilot hole adjacent the shoulder. A driving sleeve is fixedly mounted to the power shaft. A locating pin is mounted in the sleeve and engages the pilot hole to maintain the sleeve in engagement with the shoulder. The locating pin further has a flattened stem protruding radially from the drive sleeve and provides a shoulder substantially flush with the exterior surface of the driving sleeve. A hollow screw shaft is slidably journalled on the driving sleeve and a driving clutch ring is splined on the driving sleeve with an overrunning connection with the screw shaft. The driving clutch ring and the screw shaft are normally positioned and will engage each other. In addition, a spring is supplied to urge the screw shaft toward its normal position. A mesh enforcing mechanism is included resisting the movement of the driving clutch member away from its normal position. The mechanism includes an enclosing cap member having a bottom flange slidably mounted on the driving sleeve. The bottom flange of the cup member is normally seated against the flat surface of the locating pin and engages the shoulder to retain the locating pin in an operative position. A spring is also provided for resisting the further axial movement of the driving clutch member after a predetermined compression of the forcing mechanism. A control nut is threaded on the screw shaft and a pinion is slidably journalled on the power shaft for movement into and out of mesh with a ring gear of the engine to be started. Finally, a barrel member is rigidly connected to the control nut and the pinion gear.
The starter motor is activated, to cause acceleration of the drive shaft which, in turn, causes the control nut to thread itself onto the screw shaft, overcoming the initial retardation of the detent and moving the barrel assembly forwardly until the pinion enters into mesh with the engine gear. Further movement of the pinion gear is stopped by the abutment on the drive shaft. Clear rotation of the drive shaft and the screw shaft causes the screw shaft to be traversed from the abutment by the screw jack action which compresses the mesh enforcing spring and thereafter the cushioning ring until sufficient torque has been built up to initiate rotation of the engine gear. This rearward movement of the screw shaft is permitted by a counterbore and its rearward end which accommodates a snap ring. The engine gear is accelerated, and the speed of rotation of the pinion is correspondingly increased, by which the barrel and control nut may become accelerated more rapidly than the motor shaft. However, the detent latch in the control nut prevents the control nut from being threaded back to its idle position on the screw shaft. Thus, the pinion is maintained in mesh with the engine gear. When the engine becomes self-operative, subsequent rotation of the pinion and barrel assembly becomes high enough to cause the detent latch to move outwardly by centrifugal force thereby disnegaging itself from the abutment on the screw shaft. The screw shaft is, thus, permitted to be decelerated to the speed of the motor shaft by virtue of its friction connection with the driving clutch and driving sleeve which is made effective by the clutch spring. The control nut and its associated barrel and pinion consequently traverse back to an idle position where they are maintained by the engagement of the detent latch with a frusto-conical surface on the screw shaft. This device, however, is very long since the resilient member is encased in a separate housing.
None of the above aforementioned prior art starter drives, therefore, provide a compact and simple starter drive for present automotive applications.